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Hi @Rishi Rana

Hey

At ingestion time, if you create a sketch from a column and that column is not included in the ingestion, then yes, the detailed data is "lost". You can ingest the raw data directly and still take advantage of approximations at query time. The difference is performance, if the data is partially aggregated at ingestion, the queries on it will be faster.

Great thanks for detailed explanation

To add, usually people want to throw away the raw data and only store the sketch, to save space. For strings in particular, it might make sense to store both the value and the sketch. For some details, see https://intertubes.wordpress.com/2020/10/14/on-using-theta-sketches-with-druid/ .